Unitized gun mount and envelope



y 1964 .F. c. WELLS ETAL 3,142,775

UNITIZED GUN MOUNT AND ENVELOPE Filed May 1, 1961 4 Sheets-Sheet l g iil7 1 5 II HI I ?g -fip m I I a 2 i I '0 -8 I i [0 Z 4 4. I 22 s an :mtlllINVENTORS STANLEY E SWIADEK FRANK C. WELLS ATTORNEY July 28, 1964 F. c.WELLS ETAL UNITIZED GUN MOUNT AND ENVELOPE 4 Sheets-Sheet 2 Filed May 1,1961 INVENTORS STANLEY E SWIADE'K FRANK C. WELLS gym/M A T TORNE Y July28, 1964 F, c. WELLS ETAL 3,142,776

UNITIZED GUN MOUNT AND ENVELOPE Filed May 1, 1961 4 Sheets-Sheet 3INVENTORS STANLEY F SWIADEK FRANK C. WELLS m Y Z AT TO RNE Y July 28,1964 F. c. WELLS ETAL UNITIZED GUN MOUNT AND ENVELOPE 4 Sheets-Sheet 4Filed May 1, 1961 p x d mm Hg-cm ALTITUDE ABOVE SEA LEVEL IN FEET (XI000) INVENTORS STANLEY E SWIADEK BY FRANK C. WELLS l; T0 RNE Y UnitedStates Patent 3,142,776 UNITIZED GUN MOUNT AND ENVELOPE Frank C. Wells,Los Altos Hills, and Stanley F. Swradek,

Sunnyvale, Calif, assignors to Sylvania Electric Products Inc., acorporation of Delaware Filed May 1, 1961, Ser. No. 106,807 8 Claims.(Cl. 313-489) This invention relates to traveling wave tubes havingceramic envelopes and particularly to an improved mount for thecomponent parts of the gun structure of such tubes.

The method of manufacturing traveling wave tubes has progressed to thepoint that automatic machinery may be used in the assembly of thecomponent parts of the tubes. To facilitate such manufacture, tubes havebeen designed to allow annular gun electrodes and cylindrical supportsleeves, within which a cathode is mounted, to be stacked and separatedby electrically insulating spacers.

These spacers have heretofore been made of a ceramic material which hasgood electrical insulating properties but which introduces a problem ofeffecting a bond between the surfaces of the spacers and the gunelements or, alternatively, between the spacers and the cathode supportsleeves. If the usual means of attachment are used, i.e., brazing thepreviously metallized surfaces of the ceramic spacers to respectivesurfaces of the members, the sealing joint may develop minute openingsor a series of openings which can not be immediately detected. Duringsubsequent high temperature processing of mounts incorporating suchjoints, impurities within the gun elements are liberated as gases at themating surfaces of the members and metallized spacers. These gasesmigrate through the minute openings in the joint to the exterior surfaceof the envelope, or in the other direction, into its bore portion,thereby enlarging the openings and effectively destroying the seal. Thisnecessitates the time consuming and costly operation of rescaling.

Another disadvantage of prior ceramic gun construction is the tendencyof electrical breakdown between adjacent closely spaced metallizedspacer joints, especially in a low pressure environment. Such breakdownfrequently occurs in tubes in high altitude aircraft wherein arcingacross the exterior of the gun can result in total destruction of thetubes.

In accordance with our invention, the advantages of a ceramicconstruction are realized while avoiding the disadvantages mentionedabove by forming the cylindrical gun envelope with a plurality ofstraight ceramic rods having axes parallel to the longitudinal axis ofthe tube. The various gun elements are axially spaced apart within therod envelope by stacked ceramic spacers which fit snugly against therods inside the envelope. Electrical contact with the gun elements ismade by metallized joints or bands which extend between the rods atcircumferentially spaced points on the envelope. The spacing betweencontact bands on the exterior surface of the envelope is thus measuredby the circumferential as well as axial displacement.

The ceramic glaze which bonds the rods together 'into an envelopepreferably is on the outside of the envelope so that the longitudinalgrooves between rods on the inside of the envelope form convenient openpassageways to carry gaseous impurities away from the gun elementsduring the high temperature outgassing phase of tube processing.

Av primary object of this invention, then, is to provide a travelingwave tube gun structure and envelope which avoids the above describeddisadvantages of conventional ceramic stacked guns.

A more specific object is the provision of a vacuumtight envelope havingmeans for readily expelling gaseous 3,142,776 Patented July 28, 1964impurities of gun structures after assembly in the envelope.

Another object is the provision of an envelope having means providingexternal high voltage connections to gun electrodes while minimizing thedanger of arcover between adjacent electrodes.

These and other objects will become apparent from the followingdescription of a preferred embodiment of the invention, reference beingmade to the accompanying drawings in which:

FIGURE 1 is a schematic view, partially broken away, of a traveling wavetube embodying the invention;

FIGURE 2 is a transverse section of the gun structure taken on line 2-2of FIGURE 1;

FIGURE 3 is a longitudinal section of the gun structure taken along line33 of FIGURE 2;

FIGURE 4 is an enlarged view of a portion of FIGURE 2 showing details ofthe construction of the envelope wall;

FIGURE 5 is a greatly enlarged view of a portion of FIGURE 3 showingdetails of the support structure of the gun structure;

FIGURE 6 is a plot of breakdown voltagev versus the product of pressureand electrode spacing; and

FIGURE 7 shows a set of voltage breakdown curves which compare theresult of voltage breakdown on operating capabilities of traveling wavetubes. 1

In a preferred embodiment in FIGURE 1 a traveling wave tube is disclosedcomprising an elongated envelope 1 having enlarged end portion enclosinga gun assembly 3. The cathode 4 (see FIGURE 3) of the gun assemblyproduces a beam of electrons which is focused and accelerated by focuselectrode 5 and first and second anode electrodes 10 and 11,respectively, along axis A through helix 6 to collector 7. As theelectrons pass the helix, interaction between the electrons and a signalapplied to. input 8 occurs such that the signal is amplified whenextracted at output 9.

The efliciency of the tube depends upon the axial travel of theelectrons through the helix 6, and a contributing factor in achievingthis type of flow is a precisely formed gun structure. This inventionconcerns such gun structures and particularly those gunstructures'having integral enclosures adapted to and compatible withmechanized manufacturing techniques.

In accordance with the invention, the gun assembly '3 shown in FIGURES 2and 3 comprises a'cathode subassembly 12 mounted within anelectrode-spacer subassembly 13 about which is formed gun housing 14 oftube envelope 1.

For convenience in describing this invention, the term cathodesubassembly 12 is used in this specification to describe the cathodebody 28, its cylindrical support, heater, and focus electrode 5 locatedadjacent thereto. Also, the term electrode-spacer subassembly 13 refersto anode electrodes 10 and 11 (hereinafter described as rearward andforward electrodes, respectively), outer cathode support sleeve 16, andceramic spacers 17, 18, and 19 located between these members. The termforward describes the end of the assembly from which electrons areaccelerated after emission and refers to the right end of the gunstructure 3 in FIGURE 3. Similarly, rearward" designates the left end ofthe gun structure, as viewed.

Accordingly, the electrode-spacer subassembly 13 comprising electrodes10 and 11 and rearward cylindrical cathode support sleeve 16, spacedbetween annular ceramic spacers 17, 18, and 19, is mounted withinaceramic gun housing 14 such that the outer peripheral surface edges ofthe parts are in tangential contact with inner surface 42 of wall 40. Ashown in FIGURES 2 and 3, wall 40 extends axially of the parts along theentire length of the assembly and comprises a plurality of elongated,tangentially joined rods 15 having axes which are parallel to each otherand to axis A of the tube. These rods preferably have the same diameterand each makes longitudinal line contact with two adjacent rods so thattheir peripheries merge at a junction to form a cusp. These cusps areindicated at 39 in FIGURE 4 and facilitate the cleaning of the tubeparts as explained hereinafter.

The rods 15 are secured and sealed together at their junction into avacuum tight enclosure by ceramic fillets 41 made of a materialdescribed in patent application Serial No. 9,701, filed February 19,1960, and assigned to the assignee of this application. The enclosurethus formed radially confines the parts of the assembly throughout theirrespective tangential contacts with the wall 40.

The ends of rods 15 are permanently secured to the end walls 31 and 35of housing 14 to prevent axial movement of the confined parts andprovide a complete gun enclosure. As viewed in FIGURE 1, forward ends 52of these rods are mounted in contact with the rearward surface of endwall 35 in the annular space defined between the exterior radial surface53 of forward ceramic spacer 17 and interior surface 54 of annular lip55, while the peripheral surfaces of rearward ends 5-6 (see FIG- URE 3)are permanently secured in the annular space between side wall 37 ofcathode support sleeve 16 and inner surface 58 of annular lip 59 onrearward end wall 31.

Axial confinement, as well as electrical isolation of the assembly, isprovided by locating ceramic spacers 17, 18, and 19 between electrodesand 11 and cathode support sleeve 16 such that respective end surfacesof this assembly are in contact with walls 31 and 35 of gun housing 14.The assembly thus formed facilitates fabrication of gun structures byremotely operated machinery by the inherent virtue of the stacked gunarrangement, and provides a mechanically rugged support, the parts beingwedged between the end wall of the gun enclosure to prevent their axialmovement.

In detail, forward acelerating electrode 11 comprising forward cylinder20, radially extending annulus 21, and central aperture 23, is axiallyconstrained by forward spacer 17 and central spacer 18 having surfaces26 and 27, respectively, in contact with the forward and rearwardannulus surfaces 25 of annulus 21. The forward and rearward surfaces ofthe spacers in turn contact the forward end wall 35 of gun housing 14and surface 36 of annular body 29 of rearward electrode 1%,respectively.

Adjacent electrode 10, between rearward spacer 19 and rearward end wall31, is cylindrical cathode support sleeve 16 having a side wall 37 andforward wall 32 whose forward surface 33 is in contact with surface 36of rearward spacer 19. It should be noted that the term contact as usedin this specification is a relative term, depending upon many factorsone of which is the surface conditions of the parts. In maintainingclose tolerances necessary for traveling wave tube guns, it is usuallynecessary that the surfaces of the parts in contact must be ground toobtain a surface finish compatible with alignment requirements, say 32microinches. In FIGURE 5, in a greatly enlarged scale, the matingsurfaces 33 and 36 of support sleeve forward wall 32 and of ceramicspacer 19, respectively, typical of this assembly and illustrative ofthis type of joint, comprise a series of peaks 57 and valleys 61contacting one another at referenced points 64. Although these undulatedsurfaces prevent a vacuum-tight seal between the parts, the gaseousimpurities-driven from the metal electrode during the high temperatureprocess cycle are easily expelled from the tube because of theinterconnected passageways between surfaces 24 and 24a of ceramic spacer18 (see FIGURE 3).

Possible directions of the gaseous migration, in this instance, areindicated in FIGURE 5 by upwardly projecting arrow 68 and downwardlyprojecting arrow 7t If the direction is upwards, the gases eventuallyenter the longitudinally extending passageways or cusps 39 formed by thejunctions of rods forming wall 40 of the gun housing 14 and then migratefrom right to left as viewed in FIGURE 3 to be expelled from the tubethrough open fitting 63, which snugly contacts opening 62 in end wall31.

Sources of gas contamination are not, however, limited to the partscomprising electrode-spacer subassembly 13. but may include those ofcathode subassembly 12, mounted coaxially within subassembly 13. In thisarrangement (see FIGURE 3), support of subassembly 12 relative tosubassembly 13 is provided by locating the outer surface 67 of focuselectrode 5 of subassembly 12 in contact with the inner surface 76 ofside wall 37 of subassembly 13. Movement in the rearward direction isprevented by locating the surface 69 of end wall 31 adjacent to the endedge of the focus electrode 5 while forward movement is constrained byplacing rearward surface of forward wall 32.0f cathode support sleeve 16in contact with the forward portion of electrode 5.

Cathode 4, located so that upper cathode body 28 is axially adjacent tocentral aperture 71 of the focus electrode 5, is mounted to the forwardedge of inner cylindrical support member 72, which is enlarged in itsforward and rearward portions to form outwardly extending lips 72a whichare atached to the inner surface of a second support member 73.Electrical connection to heater 22 is provided by leads 66 which passthrough fitting 65 in end wall 31 to external energizing sources (notshown).

On the exterior surface of second support member 73, threecircumferentially spaced radial isolation posts, one of which is shownat 74, are provided. Each post comprises an annular ceramic member 75interconnecting two metal legs 77, and attached to the inner surface offocus electrode 5 to allow a bias voltage to be applied independent ofthe focus electrode to gate the electron beam. In steady stateoperation, however, both cathode 4 and focus electrode 5 are operated atthe same potential as illustrated hereinafter.

As shown in detail in FIGURES l3, electrical contact is made withelectrode 11 as well as with acceleration electrode 10 and focuselectrode 5 by metal bands 44, 45, and 46, preferably made by platingcopper on a thin, molybdenum-manganese film attached to and coaxia-llydisposed about rod members 15 forming wall 40 of housing 14. Leads,referenced L L and L are in turn attached at contact points 49, 56, and51 to the respective bands 44, 45, and 46 to facilitate energizing theelectrodes of the tube by external energizing sources 91, 92, and 93.

Referring specifically to FIGURES 1 and 2, electrode 11 is located suchthat its peripheral edge 78 is in contact with band 44- at contact point48, located degrees from point 49, the contact point of the band 44 andlead L Electrode 10 is energized at point 79 by band 45 which isconnected in turn at point 50 to lead L The minimum exterior distancebetween point 49 and point 50 is the circumferential spacing indicatedas S in FIG- URE 1. This spacing S illustrates that the contact bands ofaxially adjacent electrodes are separated not only by axial dimension Bbut also by a geometric arc of 180 degrees, see FIGURE 2.

As a result of the increased spacing between adjacent contacts, theprobability ofionization of the air separating bands 44 and 45 so as tosupport an arc discharge during operation of the tube is greatly reducedsince the value of voltage diiference at which arcing takes place isdirectly related to the distance (d) between the electrodes as well asthe pressure (p) of the surrounding air. This relationship is showngraphically in FIGURE 6 wherein curve 81 is a plot of breakdown voltageversus the product of pressure (p) and distance (d) in air. This curveshows that breakdown voltage falls to a minimum at a value of theparameter (p d) down of about 0.5 mm. Hg-cm., and rises rapidly forincreasing values of (PXd). Thus the curve 81 has a saddle 82 betweenits positive and negative slopes. The significance of saddle 82 to thetube designer is the fact that tubes having stacked ceramic gunconstructions and operating over a wide range of air pressures must havesufiicient distance (d) between exposed electrodes to avoid low valuesof Vs. Thus distance between electrodes in certain low pressureenvironments is a critical design factor directly related to the abilityof such tubes to operate at all.

By way of example, for the tube shown in FIGURES 1, 2, and 3, operatingin X-band frequencies (8.0 to 12.5 kilomegacycles), the breakdownvoltage-pressure characteristic is illustrated and compared by curvesshown in FIGURE 8. In this plot, the abscissa is in terms of altitudewhich is essentially inversely proportional to pressure. Curve 83represents the breakdown voltage characteristic between forwardelectrode and rearward electrode 11 of tube 1 (the most critical case)operated at 0 to 80,000 feet above sea level. Curve 84 represents asimilar voltage characteristic for a tube using a conventional ceramicstack gun having comparable electrode spacings and which depends solelyupon the axial spacing for separating the external contact points. Thehorizontal line 87 represents the voltage at which breakdown (arc-over)occurs, for the particular gun at certain operating voltages.

The electrode spacing, dimensions and operating voltages of the gun forwhich the curves of FIGURE 7 were plotted were as follows:

It will be noted that curve 84 for the conventional construction crossesthe breakdown voltage line 87 at an altitude of approximately 17,000feet whereas curve 83 crosses line 87 at approximately 63,000 feet.

It should be understood that this invention in its broadest aspects isnot limited to the specific example herein illustrated. The appendedclaims are intended to include all changes and modifications within thetrue spirit and scope of the invention.

We claim:

1. In an electron discharge device, a plurality of electrodes spacedapart along an axis, insulating spacer means separating axially adjacentelectrodes, an annular vacuumtight envelope circumscribing saidelectrodes and spacer means, said annular envelope comprising aplurality of parallel axially extending insulated rods sealed togetherin a circumferential series arrangement, and means for energizing saidelectrodes comprising an electrical conductor for each electrode andextending through said envelope, said conductors being connected toaxially adjacent electrodes and penetrating said envelope atcircumferentially spaced locations.

2. The device according to claim 1 in which said spacer means compriseannular spacers of insulating material having peripheral surfaces, eachof said electrodes extending between and being supported on adjacentsurfaces of adjacent spacers, said envelope engaging the peripheralsurface of each spacer.

3. The device according to claim 2 in which said envelope engages eachspacer at circumferentially spaced locations and defining therewith aplurality of circumferentially spaced longitudinal passages.

4. In an electron gun, a plurality of annular insulating spacers, aplurality of annular electrodes stacked axially between and engaged withsaid spacers, an envelope formed about and in contact with said spacers,and means for energizing said electrodes comprising contact bandsdisposed in and integral with said envelope in tangential contact with alike number of said electrodes, with adjacent bands circumferentiallyspaced degrees, said envelope comprising a plurality of insulating rodscoupled together in permanent tangential engagement having tangentialline contact with peripheral edges of each of said spacers andelectrodes.

5. In a traveling wave tube adapted to operate in an environment havingsubstantial changes in atmospheric pressure, an electron gun and anenvelope containing said gun, said gun having an axis, a cathode forproducing a beam of electrons along said axis, a cylindrical sleevesupporting said cathode, a plurality of annular electrodes for focusingand accelerating said beam, and a plurality of insulating spacersstacked in engagement with and separating said sleeve and electrodes;said envelope comprising a plurality of insulating rods having agenerally circular cross section and coupled together in permanent,tangential engagement and with axes parallel with said axis and being intangential contact with said sleeve and with said electrodes, and meansto facilitate energizing said electrodes comprising contact bandscoaxially disposed about said rods in tangential contact with saidelectrodes, with adjacent bands circumferentially spaced apart by 180degrees.

6. In a traveling wave tube adapted to operate in an environment havingsubstantial changes in atmospheric pressure, an electron gun and anenvelope containing said gun, said gun having an axis, a cathode forproducing a beam of electrons along said axis, a cylindrical sleevesupporting said cathode, a plurality of annular electrodes, means forenergizing said electrodes to focus and accelerate said beam, and aplurality of insulating spacers stacked in engagement with andseparating said sleeve and said electrodes; said envelope comprising aplurality of insulating rods coupled together in permanent, tangentialengagement and with axes parallel with said axis and being in tangentialContact with said sleeve and said electrodes, said means for energizingsaid electrodes comprising con tact bands coaxially disposed about saidrods in tangential contact with said electrodes, adjacent bands beingcircumferentially spaced apart by 180 degrees.

7. In an electron discharge device adapted to operate in an environmenthaving substantial changes in pressure, an electron gun and an envelopecontaining said gun, said gun having an axis, a cathode for producing abeam of electrons, a plurality of electrodes for focusing andaccelerating said beam along said axis, and a plurality of insulatingspacers stacked in engagement with and separating said electrodes; saidenvelope comprising a plurality of insulating rods having a generallyrounded cross section and coupled together in permanent, tangentialengagement with said spacers and said electrodes; and means tofacilitate energizing said electrons comprising contact bands coaxiallydisposed about said rods contacting a like number of electrodes,adjacent bands circumferentially spaced on said envelope.

8. In an electron discharge device, an electron gun and an envelopecontaining said gun, said gun having a means for producing electrons, aplurality of electrodes for focusing and accelerating said beam, and aplurality of insulating spacers stacked in engagement with saidelectrodes; said envelope comprising a plurality of insulating memberscoupled together about said spacers and said electrodes, and contactmeans integral with said envelope comprising a plurality ofcircumferentially spaced metal bands, each of said bands beingelectrically connected to one of said electrodes.

References Cited in the file of this patent UNITED STATES PATENTS1,955,899 Zworykin Apr. 24, 1934 2,808,528 Martin Oct. 1, 1957 2,859,372Stangl Nov. 4, 1958 2,938,133 Hueter May 24, 1960

8. IN AN ELECTRON DISCHARGE DEVICE, AN ELECTRON GUN AND AN ENVELOPECONTAINING SAID GUN, SAID GUN HAVING A MEANS FOR PRODUCING ELECTRONS, APLURALITY OF ELECTRODES FOR FOCUSING AND ACCELERATING SAID BEAM, AND APLURALITY OF INSULATING SPACERS STACKED IN ENGAGEMENT WITH SAIDELECTRODES; SAID ENVELOPE COMPRISING A PLURALITY OF INSULATING MEMBERSCOUPLED TOGETHER ABOUT SAID SPACERS AND SAID ELECTRODES, AND CONTACTMEANS INTEGRAL WITH SAID ENVELOPE COMPRISING A PLURALITY OFCIRCUMFERENTIALLY SPACED METAL BANDS, EACH OF SAID BANDS BEINGELECTRICALLY CONNECTED TO ONE OF SAID ELECTRODES.